Exotel is "Software as a Service" (SaaS). And in SaaS, they say that service is more important than Software. So, when it is all about service, surely, there is service tax and we do charge it. It is 14.00% (Government mandated) at the time of writing this article and may change. 

Exotel is prepaid, similar to a Prepaid SIM card connection. When operators charge you for a talk time recharge, they actually also include service tax in it. For example: 500 Rs recharge is actually 445 Rs base amount + 55 Rs Service tax. But, they load your SIM card with 500 Rs talktime anyway. Exotel does the same thing too. When you pay, we collect service tax as an advance too. 

But unlike prepaid, you do actually get an invoice for your exotel account. This is sent once a month and you will notice a service tax component in this invoice too. But this does not mean we are charging service tax twice. Infact, this invoice is already paid for and this invoice is really just for your books. 

So, If you paid 114.00 rs: 100 rs goes as exotel credit and 14.00 sits as service tax advance payment in our accounting software. Lets say your first month bill is 50 Rs, then we add 7.00 Rs as Service tax and send you a bill for 57.00. 

That is how we marry prepaid with invoice!